Method for simultaneously induction heating a plurality of elements



METHOD FOR SIMLTANEOUSLY INDUCTION HEATING A PLURALITY 0F ELEMENTS Original Filed June 30, 1943l v Oct. l0; 19504 l n A. BIERWIRTH y 2,525,336

INVENTOR RUDDLPH ABI HWIRTH j BY ATTORNEY Patented Oct. 10, 1950 METHOD FOR SIMULTANEOUSLY INDUC- TION HEATING A PLURALITY F ELE- MENTS Rudolph A. Bierwirth, MountProspect, Ill., assignor to Radio Corporation of America, a corporation of Delaware Original application 'June 30, 1943, Serial No.

492,813. Divided and this application November 14, 1947, Serial No. 786,088y

4 claims. (ci. 21a- 13) This invention relates to a method of induction `1 heating, and more particularly to a kmethod -of` simultaneously heating a plurality of conductive elements by induction with high eiiciency, the present application being a division of my copending application Serial No. 492,813, led June 30, 1943, and issued June 8, 1948 as Patent Number 2,442,968.

. In the manufacture of radio tubes, for example, the leads from the several electrodes are brought down through hollow terminal pins or prongs on the tube envelope and connection of the tube to an external circuit is made through such pins. The electrode leads are usually soldered to the prongs by means of solder therewithin. Heretofore, in order to melt the solder, it has been customary to heat the prongs b'y means of a gas flame or the like, but this is not altogether satisfactory since it is difficult to control the flow and setting of the solder when a flame is used as the source of heat.

The primary object of my present invention is to provide an improved method of heating radio tube prongs and other similar conductive elements which will not be subject to the disadvantages found in prior art methods.

More particularly, it is an object of my present invention to provide an improved method as aforesaid which will heat the work rapidly and with high eiciency.

Another object of my 4present invention is to provide an improved method of heating radio tube prongs as above set forth wherein the heating is accomplished by induction and wherein efficient coupling between the heating apparatus and the work is effected.

In accordance with my present invention, the tube base pins or prongs are coated internally with solder and the solder is melted and caused to run to the ends of the pins for soldering in the lead` wires. The pins are heated by induction by placing around them a small, helical inductor carrying radio frequency current. The prongs are usually arranged in a circular path and the inductor is arranged concentrically therewith, being spaced from the pins only a short distance. Even under this condition, however, and particularly where the pins or prongs are made of brass or other non-ferrous material, the heating eiliciencyv coupling between the inductor and the prongs., To overcome this, I place within the circle of pins a concentrator in the form of a properly shaped block or mass of copper. This mass is inductively related to both the prongs and the inductor. When radio frequency current is passed through the inductor, it induces currents in the concentrator as Well as in the prongs, The current in the concentrator, in turn, induces additional current in the prongs, thereby intensifying the current in the latter and causing all of the prongs to rbecome heated rapidly and simultaneously to the melting temperature of the solder. The melted solder then runs down to the ends of the pins and unites the lead wires to their respective pins or prongs.

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, as well as additional objects and advantages thereof, will best be understood from the following description, when read in connection 'with the accompanying drawing in which Figure 1 is a side elevation of one form of heating device for carrying out the method of my present invention and shown applied to the prongs 0f a radio tube. l

Figure 2 is a bottom plan view thereof,

Figure 3 is a fragmentary, sectional view of one of the prongs with the lead wire therein prior to the soldering operation,

Figure 4 is a View similar to Figure 3 but showing the lead Wire soldered to the prong, and

Figure 5 is an enlarged, fragmentary view of a portion of the apparatus shown in Figure 2.

Referring more particularly to the drawing, wherein similar reference characters designate corresponding parts throughout, there is shown a radio tube I provided with a plurality of discrete, hollow, base pins or prongs 3 spaced from each other in a circular path and with an aligning plug 5 formed with an aligning key l, as best seen in Figs. 2 and 5. A lead wire 9 extends into each of the prongs 3 and connects with a separate one of a plurality of electrodes within the envelope of the tube I in well known manner.

In order to provide good electrical contact between the leads 9 and their respectively associated prongs 3, each of the prongs or pins 3 may be will not be very great because ofthe relativelypoor lined withrelatively low melting point solder I I.`

3 The solder may be heated to melting temperature by means of a primaryinductor I3 of one or more turns connected through a transformer I5 to a source of high frequency electrical energy I1, such as a radio frequency oscillation generator of the vacuum tube type. The inductor I3 is placed around the prongs 3 in fairly close proximity thereto so as to obtain close coupling between the inductor and the several prongs. Since, however, the inductor I3 does not surround each of the several prongs individually, the magnetic coupling between the inductor I3 and the prongs 3 will not be very close.

To increase the eiciency of coupling, I provide a concentrator or focus inductor I9 in the form of a block or mass of copper which fits over the aligning plug 5 and its key I and is arranged concentrically with the coil I3 and the circular path of the prongs 3. The concentrator I9, which is essentially a secondary inductor, is provided with a plurality of longitudinally extending, circumferentially spaced, peripheral slots or grooves 2l corresponding in number to the number of prongs 3. As clearly seen from Figs. 2 and 5, the arrangement is such that each of the lgrooves 2I receives a separate prong 3 in substantially concentric relation therewith and in close proximity thereto, with the projections 23 on the concentrator I9 between the grooves 2| extending into the spaces between the respective prongs. In this way, close magnetic coupling is obtained not only between the concentrator I9 and the prongs 3, but between the concentrator I9 and the primary inductor I3 as well, so that the inductor I3, the prongs 3, and the concentrator I9 are all closely coupled together magnetically.

Upon application of power to the inductor I3, the current flowing therein, represented by the arrows A, induces current in each of the prongs 3,

represented by the arrows B, and current in the concentrator I9, represented by the arrows C. The latter, in turn, also induces current in each of the prongs 3, represented by the arrows D. It will be seen, therefore, that the current B, D in each of the prongs 3 is much more intense than would be the case if the concentrator I9 were omitted and only the current represented by the arrows B were induced in the prongs. The induced currents B, D heat all of the prongs simultaneously and relatively rapidly to the melting temperature of the solder II, whereupon the solder flows down toward the ends of the pins to bond the lead wires 9 to their respective prongs 3, as shown in Fig. 4.

In one installation according to the present invention, the inductor I3 was made of 1A; inch O. D. copper tubing through which water was circulated for cooling. The concentrator I9 was constituted by a block of copper with grooves 2i cut therein to clear the pins 3 and a hole provided at the center to accommodate the aligning plug and its key. Thus, the block I9 formed a closed, single turn ring. The block I9 was of suincient mass to permit the heat developed therein to be conducted away and dissipated into the surrounding air. It will be noted that the current C induced in the concentrator block I9 flows on the outer skin thereof and since it is in a direction opposite to that of the current A in the inductor I3, it sets up a magnetic field which opposes that produced by the current A. Thus, the field inside of the concentrator is practically zero while the eld between the concentrator and the inductor or coupling coil I3 is more intense than if the concentrator were not present. By

asaas way of example, it may be pointed out that, with a tubehaving brass pins vor prongs 3, a certain current through the coupling coil heated the pins to the soldering temperature in approximately 4 seconds with an overall eciency of approximately 30.5 percent. With the concentrator removed, the heating time required was l2 seconds for the same current through the coupling coil and the efficiency was found to be about 20 percent. The current was supplied to the inductor I3 in each case at a frequency of 1,000,000 cycles per second.

Although I have shown and described in detail one form of apparatus for practicing my inven- `tion, it will undoubtedly be apparent to those skilled in the art that many other forms thereof, as well as variations in the particular one described, are possible. Thus, the concentrator I9 may be of any suitable shape as, for example, cylindrical, with the grooves 2I omitted. Also, the concentrator may be water cooled if found necessary. Furthermore, in some cases, it may be found desirable to place the inductor I3 within the circle defined by the prongs 3 or other similar elements to be heated, and the concentrator I9 disposed around the prongs or the like. Other similar changes will, no doubt, readily suggest themselves to those skilled in the art. I therefore desire that my invention shall not be limited except insofar as is made necessary by the prior art and by the spirit of the appended claims.

What I claim is:

1. The method of heating a plurality of workpieces of electroconductive material with the aid of two inductively related inductors one of which is adapted to be inserted coaxially within the other and one of which is a closed inductor, which comprises bringing said vworkpieces and said inductors all into close inductive relation with each other with the workpieces in spaced substantially parallel relation to each other between said inductors, conforming at least one of said inductors to each of said workpieces to enhance the inductive coupling therewith, and passing a high frequency alternating current through one of said inductors whereby to induce current in both said workpieces and the other of said inductors, the current so induced in said workpieces serving to effect partial heating of said workpiecesy and the current in said other inductor serving, in turn, to induce additional current in said workpieces for eifecting further heating of said workpieces.

2. The method of heating a plurality of work- Y pieces of electroconductive material with the aid of a primary inductor and a closed secondary inductor disposed co-axially within and in close inductive relation to said primary inductor which comprises placing said workpieces in spaced substantially parallel relation to each other between said inductors and conforming said closed secondary inductor to each of said workpieces whereby to bring said workpieces and each of said inductors all into closely coupled relation with each other, and passing a high frequency alternating current through said primary inductor whereby to induce current in both said workpieces and said secondary inductor, the current so induced in said workpieces serving to effect partial heating of said workpieces and the current induced in said secondary inductor serving, in turn, to induce additional current in said workpiecs for eiecting further heating of said workpieces.

3. The method of heating, with the aid of a primary inductor and a closed secondary inductor rent through said primary inductor whereby to simultaneously induce current in each of said Workpieces and in said secondary inductor, the

current so Ainduced in each of said workpieces serving rtoeffect partial rheating of said workpieces, and the current in said secondary inkdu'ctor serving, in turn, to induce additional current in each of said workpieces for effecting further heating of said workpieces.

4. In the manufacture of radio tubes including a plurality of hollow terminal prongs and a plu.-Y

rality of electrode K leads extending into said prongs, the method of bonding said leads totheir respective I prongs, which comprises lining said prongs with a relatively low melting point solder,

` subjecting all of said prongs simultaneously vto a radio frequency magnetic field between anouter primary inductor and an inner closed secondary inductor with said prongs therebetween whereby to induce insaid prongs heating currents conforming said secondary inductor to said prongs inY spaced substantially concentric relation thereto and projecting therebetween to increase the iiow of said induced currents insaid prongs whereby to produce sufficient rheat therein. relatively rapidly-to melt said solder, and subsequently removing said magnetic field to permit said solder to harden and bond said leads to their respective prongs. i

RUDOLPH A. BIERWIRTH.

REFERENCES CITED The following references are of record in the ile` of this patent:

- yUNITED STATES PATENTS Number l Name Date 1,862,120 Northrup June '7, 1932 1,929,212 lONeill Oct. 3, 1933 1,997,741 Northrup Apr. 16, 1935 2,408,229 Roberds Sept. 24, 1946 

